The present invention relates to a method of suppressing a pinging phenomenon affecting the operation of an internal combustion engine and, more particularly, to such a method calling on a "fuzzy" logic control of an engine operation parameter.
It is known that certain abnormal combustions of the air/fuel mixture introduced into an internal combustion engine give rise to high-pressure waves and hence to an acoustic noise known as "pinging". When the latter is intense, it may result in impairments of the engine, such as erosion of the cylinder head and pistons, fractures of the piston lands and rings, failure of the cylinder head gasket or deterioration of the valves, for example.
As known for example from the publication "Adaptive Spark Control with Knock Detection" published by the Society of Automotive Engineers under the number 840447, the operating diagram of a conventional device designed to prevent such deteriorations of the engine under the effect of the pinging phenomenon has been represented in FIG. 1 of the attached drawing. The device comprises a pinging sensor 1, of the accelerometer type for example, fixed to the engine so as to be sensitive to the pinging arising in each cylinder of the engine, the sensor delivering a signal processed in a conditioning stage 2 before being delivered to means 3 for calculating an ignition advance reduction R.sub.A, as a function of various strategies, these means correcting, as a function of the calculated reduction, the instant of ignition of the engine spark plugs located in the cylinders in which the pinging was detected. It is known that such a reduction has the effect of suppressing the pinging. When the latter has disappeared, the calculating means permit a return of the ignition advance to the nominal value.
More precisely, in accordance with a current technique used for detecting pinging, during each engine cycle, the average energy of the pinging, in each of the cylinders in which it occurs, is calculated and this average energy (clqmoy) is compared with the instantaneous pinging energy (valclq) as illustrated by the graph of FIG. 2. A band separating a region situated to its right and in which pinging is supposed to exist from a region situated to its left in which pinging is supposed not to exist, has been represented in this graph. The separation band has a slope (clqgn) and an origin abscissa (clqof) for its right boundary.
Hence, pinging is supposed to be present if: EQU clqmoy&lt;(valclq-clqof).times.clqgn
In the presence of pinging thus detected, the device of FIG. 1 orders a sizeable advance reduction R.sub.A (of about 7.degree. for example) in the cylinder which is pinging, in the following engine cycle, this reduction possibly being repeated once should the pinging persist, the instant of ignition being thus brought closer to the top dead centre (TDC) by 14.degree. in total. The return to the nominal value of ignition advance takes place later, after the pinging disappears, at a rate of approach of about 1.degree. every 2.5 seconds for example. Other corrections, applied more "slowly", may be provided for in order to tune the ignition for the fouling and ageing of the engine, for the loss in efficiency of the cooling circuit, for the quality of the fuel, etc.
The technique described above for suppressing or lessening pinging has various disadvantageous limitations. As was seen earlier in connection with the graph of FIG. 2, in accordance with this technique, detection of pinging is of the "all-or-nothing" type: pinging does or does not exist and hence no distinction is made between nascent pinging and intense pinging. Therefore, the amplitudes of the advance reductions due to the corrections described above are the same, whatever the intensity of the pinging. This results in impairment of the performance of the engine, in particular as regards torque or fuel consumption, due to a non-optimal setting of the angle of ignition advance.
With the introduction of fuzzy logic control, several attempts have been made to implement this technology in processes where old control techniques could be improved, particularly by the "smoothing" brought by fuzzy control. Japanese published application JP-A-1100377 suggests use of fuzzy theory to control ignition timing in idling conditions, based upon engine rotational speed. More generally, JP-A-1113574 proposes the use of fuzzy logic control for any function of an engine controller (ignition timing, air/fuel ratio control, . . . ) with capability to change the membership function according to detection of transient conditions. More recently, JP-A-2188676 teaches the use of fuzzy inference in obtaining a lead angle, for correcting ignition time, from engine load, speed and knock information, to cope with engine load changes.